Natural gas is obtained in an offshore extraction facility, for example, and transported ashore via a pipeline. A large-scale chemical plant is located on land, by which the natural gas is separated into its constituents, which may be long-chain and short-chain hydrocarbon compounds, for example. The portion of the natural gas consisting of the short-chain hydrocarbons, after pressurizing, is fed to a natural gas supply network and offered on a natural gas market. The distribution of the natural gas is based on the consumption of the natural gas supply network so that countries which are not connected to the natural gas supply network, for example, are cut off from the natural gas market. The reasons for why these countries are not connected to the natural gas supply network lie in their geographical location, for example, which makes a connection of these countries to the natural gas supply network technically difficult or impossible. If this country is accessible from the sea, for example, then the possibility presents itself of supplying this country by the use of shipping. For this, the natural gas is liquefied by a natural gas liquefaction plant (also referred to as a liquid natural gas (LNG) plant) in the extraction area, consigned to a ship, transported by ship from the extraction area to the consumer country and regasified there for distribution.
Cited document WO 2005/024188 A2 describes a turbocompressor train which has a gas turbine and also a generator and a steam turbine, wherein the steam turbine together with the generator can be coupled to the turbocompressor unit.
A method for operating a single-shaft gas and steam turbine plant with overrunning clutch is known from cited document EP 1 710400 A1.
Cited document U.S. Pat No. 5,386,687 A discloses a turbocompressor train with a drive unit which has a gas turbine and also a generator and a steam turbine, wherein the steam turbine acts upon the generator of the turbocompressor unit.
Patent application WO 02/49998 deals with the improvement of a synthesis gas plant by installation of increased compressor power also by compressors being coupled to drive trains in different variants.
The natural gas liquefaction plant is located in the extraction area either on land or near to the coast in coastal waters on a floating island. In the natural gas liquefaction plant, the natural gas is cooled in a refrigeration cycle to such a degree that it can be liquefied. The refrigeration cycle conventionally has two turbocompressors which are driven by a gas turbine or an electric motor. In the case of an annual production of the natural gas liquefaction plant of 5 to 10 megatons per year, single-shaft gas turbines are used, wherein the two turbocompressors are intercoupled by their shafts. Conventional single-shaft gas turbines do not adequately deliver torque at low rotational speeds so that the two turbocompressors cannot be started by them. Assistance is created in this case by the use of a booster starter motor which is coupled to the turbocompressor and provides additional torque during the starting process so that the turbocompressors can be started by the gas turbine together with the booster starter motor.